Solar energy utilization by PV has become a vital source of renewable energy (RE) [1]. There are many factors affecting the performance of the PV system. The tilt angle (TA) of solar panels is one of these factors which can effectively enhance the electrical energy production. In the last five years, numerous researches have been conducted in various countries around the world to determine the OTA for solar panels [2].
These studies have used various techniques and software to compute the OTA. These include mathematical modeling and numerical simulations, experimental approaches, and Artificial Intelligence (AI)-based methods. Also, these studies nearly covered most of the world countries such as China, Spain, India, Brazil, Turkey, Algeria, Iraq, Malaysia, Pakistan, Saudi Arabia, Iran, Morocco, Libya, Egypt, Ecuador, Ethiopia, and Uganda. For instance, in Turkey [3], Cagman found that PV panels tilted at a 30° angle at Bursa city that has latitude angle (LA) of 40.1885° N generates more energy than that is tilted at 13° by 42.17 kWh/year or 2.45%, with CO2 production discount of 495 tons for a period of twenty five years. This is agreed with that the TA is very near to the Oulimar, and Bellaoui [4] implemented a study to find the OTA in Adrar, Algeria that has LA of 27.874° N. The study was based on collecting data for eleven years. The outcomes of the study stated that the OTA is 28°, which is very near to the LA.
In [5], Ponce-Jara and Rus-Casas suggested the use of a tracking system for PV to improve the efficiency of the PV panels in Ecuador. The authors of the current study believe that a tracker system is not suitable for PV panels from the practical point of view. A remarkable work was done in Brazil by Cavalcanti and Batista [6] in which a comparison has been made between three PV systems which were installed in the state of Ceará, Brazil which has LA of -3.731862o. The first and second systems are fixed at TAs of 18o and 22o and the third system has a solar tracker. The total cost of the three systems were 1428.47$, 1428.57$ and 1921.43$ respectively. The system with TA of 18o has the lowest performance, and the system with TA 22o has a performance very near to that with solar tracker but with lesser costs but without the extra cost of the tracker.
Memon and others in [7, 8] presented a numerical analysis using MATLAB/Simulink to find the OTA for a 1 MW PV system that was previously installed at 15o TA at Sukkur IBA university in Pakistan that has latitude of 27.73o N. The OTA was found to be 29.5o. Although is OTA is very near to the LA, but the authors of the current study are sure that the OTA is slightly less that the LA. Xu a and Longin [9] investigated the OTA for areas with high elevation in Batang County, Sichuan, and China that has latitude 30.0054° N. They used a TA of 40o for best performance. In [10], a comparison between two TAs is implemented in Kelantan, Malaysia. The first TA is 40o and the other panel is horizontal. The TA of 40o had better performance than the horizontal surface, which is logical sine the horizontal surface is very far from the LA. A thorough study has been implemented in [11] to find the OTA for different cities in Iraq. The study used a data that were collected in 19 years and suggested that the TAs for winter months are different from those for summer months. The study ended by suggesting an annual OTA for 18 cities in Iraq.
In [12], a study has been made to find the annual OTA for Yazd city in Iran (Latitude 31.54o) and it was found to be 29.38o, which is convenient since it is slightly less than the Ashetehe [13] computed the seasonal and yearly OTAs for Bahir Dar city (Latitude 11.5742° N) in Ethiopia. Yadav [14] suggested that there is a link between OTA and the LA which is stated by many other authors. Mamun, et al. in [15] suggested a 15o is the best TA for all cities in Malaysia (LA 4.2105° N). Similar work was done in [16] in Punjab, Pakistan which has LA of 31.1471° N but suggested the same TA of 15o which far from the value of the Karinka and Upadhyaya [17] stated that if the PV panels are not tilted at monthly OTA, there will be an energy loss of 12%. Morad and Al-Sayyab [18] a study had been implemented compute the annually and monthly OTA at three cities in Iraq. These cities are the capital which has LA of 33.33°, Tikrit that has LA of 34.58°, and Diyala which has LA of 33.233°. The authors suggested that one OTA of 31 for the three cities. Tamoor and Habib [19] a studied has been implemented in Pakistan suggested that a TA of 15o is acceptable for PV panels. Obiwulu and Erusiafe in [20] used 6 systems tilted at different TAs in Nigeria, and suggested that a TA of 16.8o gives the best performance. Ashetehe [21] continued his work made in [13] and suggested OTA for some cities in Ethiopia. The OTAs were computed in some cities in SA in by Mansour [22] and he suggested that for the city of Riyadh that has LA of 24.7136° N, a TA of 22.7 was chosen to be the best TA.
Farahat [23] selected TAs of 30°, 20° and 25° for some cities in SA. Sharma [24] suggested the monthly OTA for Pradesh, India that has LA of 31.7° N. Sahin [25] used ANN to compute the OTA in Turkey and stated that the OTA can rise SR by 34%. Taha and Hameed [26] computed the OTA in Duhok University that has LA of 36.862o and it its value was 32.7o. Nfaoui [27] computed the OTA that gives the optimal SR in Morocco. Abdelaal and et al. [28] conducted through simulations to determine the OTA for each day, each month, each season, and for the whole year. They computed the OTA in some cities in EGYPT. Similar works can be found in references [1, 2, 29–41] which they focused on the computation of the OTA that gives the optimal SR in different countries.
Recently heuristics methods have been used to get the OTA. For example in [42], the Particle Swarm Optimizer (PSO) and Bee colony (BC) were used to calculate the OTA. The results shows that a very slight difference between the two methods. Most of the pervious methods showed that the OTA is very near to the LA and the difference between the two computed angles in the range of 1 to 3 degrees.
This work is focused on estimating the OTA by GTA, beside with an experimental work on three PV tilted systems. Also other MHT were used to compare the results with that obtained from GTA.
The main contributions of the present work are i) firstly is to explain the significance of the TA that gives nearly a constant SR all over the year, otherwise money lost will results in, ii) The use of GTA and other 8 MHTs to compute the OTA, and iii) The results are verified by an experimental work done by using 3 PV panels placed at 3 different tilt angles.
This paper is sorted as follow; the first section of the paper displays the previous work done in the computation of the OTA. Section 2 reviews the basic relations of SR on both horizontal and tilted surfaces. Section 3 analyzes the importance of the correct TA that gives a nearly constant SR all the year. Section 4 investigates the application of the GTA beside with 8 different MHTs to compute OTA. The 8 MHTs are genetic algorithms (GA), Particle Swarm (PS), Harmony Search (HS), Ant colony (AC), Cuckoo Search (CS), Bees Colony (BC), Fire Fly (FF), and Grey Wolf (GW). Section 5 shows the simulation results of these different techniques. The final section presents the experimental work that has been implemented on 3 different TAs.